图片.png
logistics的理论知识，请参见下方博文：
Logistic回归原理及公式推导
import numpy as np
import matplotlib.pyplot as plt
def loadDataSet():#定义一个创建数据集函数
dataMat = []
labelMat = []
fr = open('Ch05/testSet.txt')
for line in fr.readlines():
lineArr = line.strip().split()
dataMat.append([1,float(lineArr[0]),float(lineArr[1])]) #这里因为原数据是二维的，只有x1和x2，为了方便后面的计算，引入一个x0，并全部赋值为1
labelMat.append(int(lineArr[2]))#建立标签列
fr.close()
return dataMat,labelMat
def sigmoid(inx):#定义sigmoid函数
return 1/(1+np.exp(-inx))
def gradAscent(dataMatIn,classLabels):
dataMatrix = np.mat(dataMatIn)#100*3的矩阵
labelMat = np.mat(classLabels).T#100*1的矩阵
m,n = dataMatrix.shape
alpha = 0.001
maxCycles = 500
weights = np.ones((n,1))#3*1，定义初始回归系数
for k in range(maxCycles):#迭代调整回归系数
h = sigmoid(dataMatrix*weights)#100*1的矩阵，利用回归系数计算样本预测值
error = (labelMat - h)#100*1的矩阵，计算每个样本的误差(实际值-预测值)
weights = weights + alpha*dataMatrix.T*error#3*1的矩阵，调整回归系数weights
#dataMatrix.T是3*100的矩阵，error是100*1的矩阵，双方经过300次乘法相加，得到3*1的矩阵
return weights#输出最终的回归系数
def plotBsetFit(wei):
weights = wei.getA()#将矩阵转化为np.ndarry对象
dataMat,labelMat = loadDataSet()
dataArr = np.array(dataMat)
n = dataArr.shape[0]
xcord1 = []; ycord1 = []
xcord2 = []; ycord2 = []
for i in range(n):
if int(labelMat[i]) == 1:
xcord1.append(dataArr[i,1])
ycord1.append(dataArr[i,2])
else:
xcord2.append(dataArr[i,1])
ycord2.append(dataArr[i,2])
fig = plt.figure()
ax = fig.add_subplot(111)
ax.scatter(xcord1,ycord1,s=30,c='red',marker='s')
ax.scatter(xcord2,ycord2,s=30,c='green')
x = np.arange(-3,3,0.1)
y = (-weights[0]-weights[1]*x)/weights[2]
#这里，令sigmoid函数等于0，求出x1和x2的关系，即为要画的分割线
ax.plot(x,y)
plt.xlabel('X1')
plt.ylabel('X2')
plt.show()
#以上梯度算法中，每次迭代都要遍历所有的数据，每次都有300次的乘法，如果数据量大，很容易
#累死，下面优化为随机梯度算法，即每次迭代只选择一个样本
def stocGradAscent0(dataMatrix,classLabels):
m,n = dataMatrix.shape
alpha = 0.01
weights = np.ones((n,1))
for i in range(m):
h = sigmoid(sum(dataMatrix[i]*weights))
error = classLabels[i] - h
weights = weights + alpha*dataMatrix[i]*error
return weights #注意，这里返回的weights是1*3的np.ndarry形式，不是矩阵形式
#因此在调用画图函数时，需进行转换和转置
#调用画图函数可以看出，迭代效果没有全数据集迭代好，下面尝试对步长进行优化
def stocGradAscent1(dataMatrix,classLabels,numIter=150):
m,n = dataMatrix.shape
weights = np.ones((n,1))
for j in range(numIter):#重复迭代全集样本
dataIndex = list(range(m))
for i in range(m):#随机迭代每一个样本
alpha = 4/(1+j+i)+0.01 #s随着迭代调整步长
randIndex = int(np.random.uniform(0,len(dataIndex)))#随机选择一个样本
h = sigmoid(np.sum(dataMatrix[randIndex]*weights))
error = classLabels[randIndex] - h
weights = weights +alpha*dataMatrix[randIndex]*error
del dataIndex[randIndex]
return weights
#画图，可以看出效果要比上个随机梯度好很多
从疝气病症预测病马的死亡率
def classifyVector(x,weights):#定义一个分类函数，利用sigmoid计算属于1的概率
prob = sigmoid(np.sum(x*weights))
if prob > 0.5:
return 1
else:
return 0
def colicTest():
frTrain = open('Ch05/horseColicTraining.txt')
frTest = open('Ch05/horseColicTest.txt')
trainingSet = []; trainlabels = []
for i in frTrain.readlines():#加载训练数据
ilist = i.strip().split('\t')
trainingSet.append([float(x) for x in ilist[:-1]])
trainlabels.append(float(ilist[-1]))
frTrain.close()
trainWeights = stocGradAscent1(np.array(trainingSet),trainlabels,1000)
#利用训练数据生成一组最优回归系数
error = 0; numTest = 0
for i in frTest.readlines():
numTest += 1
ilist = i.strip().split('\t')
pard = classifyVector(np.array([float(x) for x in ilist[:-1]]),trainWeights)
#利用测试数据和最优回归系数，判定分类
if int(pard) != int(ilist[-1]):
error += 1
frTest.close()
errorRate = float(error)/numTest
print('the error rate of this test is:%f'%errorRate)
return errorRate
def multiTest():
numTest = 10; errorSum = 0
for i in range(numTest): #重复10次，求平均错误率
errorSum += colicTest()
print('after %d iterations the average error rate is:%f'%(numTest,errorSum/numTest))
#程序运行可能会报以下警告
RuntimeWarning: overflow encountered in exp python
这是因为float存储的位数有限制，计算过程中对于超出位数限制的，python会进行截取。不影响运算。如果要想避免，可了解下python的bigfloat
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